@incollection{SampangiRoentzsch, author = {Sampangi, Shiva Kumar and R{\"o}ntzsch, Lars}, title = {Electrolysis - Proton-exchange membrane electrolyzer | Proton exchange membrane water electrolysis: State-of-the-art technique and systems}, series = {Reference Module in Chemistry, Molecular Sciences and Chemical Engineering}, booktitle = {Reference Module in Chemistry, Molecular Sciences and Chemical Engineering}, editor = {Reedijk, Jan}, publisher = {Elsevier}, isbn = {978-0-12-409547-2}, doi = {10.1016/B978-0-323-96022-9.00237-1}, language = {en} } @misc{ReimannKohlenbachRoentzsch, author = {Reimann, Ansgar and Kohlenbach, Paul and R{\"o}ntzsch, Lars}, title = {Development of a novel quasi-2D PEM Electrolyzer Model in Modelica}, series = {Proceedings of the 15th International Modelica Conference 2023, Aachen, October 9-11}, journal = {Proceedings of the 15th International Modelica Conference 2023, Aachen, October 9-11}, publisher = {Link{\"o}ping University Electronic Press}, issn = {1650-3686}, doi = {10.3384/ecp20463}, pages = {9}, abstract = {To increase the efficiency of PEM electrolysis, simulation models are required that accurately describe the system's electrochemical and thermal behavior in a computationally efficient manner and are thus suitable for developing control strategies. Therefore, a pseudo-2D PEM electrolyzer model is presented in this paper, which is a compromise between the previously developed models regarding their model complexity. The electrochemical behavior is described with equations commonly used in the literature and the thermal behavior with correlations for gas-liquid heat transfer. Preliminary validation indicates that the model can describe the electrochemical behavior and thermal dynamics of a PEM electrolysis stack with good accuracy.}, language = {en} } @misc{DanilaKunzRoentzsch, author = {Danila, Kevin and Kunz, Philip and R{\"o}ntzsch, Lars}, title = {Dynamic operation of low-temperature electrolyzer systems in modular large-scale chemical plants}, series = {Chemie - Ingenieur - Technik : CIT}, volume = {2025}, journal = {Chemie - Ingenieur - Technik : CIT}, publisher = {Wiley-VCH GmbH}, issn = {0009-286X}, doi = {10.1002/cite.202400140}, pages = {1 -- 11}, abstract = {As one of the main contributors to the greenhouse gas emissions worldwide, the reduction of emissions in chemical industry is indispensable. The production of hydrogen from renewable energy sources using water electrolysis can contribute to this goal. However, the dynamic character of renewable energy sources leads to major challenges regarding the dynamic operation of the production process. Here, a model of a modular low-temperature electrolyzer plant is presented. The effect of available time resolution of the source electricity as well as the impact of the integration time step is studied. With the presented model the positive effect of load-dependent operation of modular electrolyzer plants with fluctuating availability of source electricity on the total hydrogen output is demonstrated.}, language = {en} } @misc{SharmaRoentzschShahi, author = {Sharma, Prerana and R{\"o}ntzsch, Lars and Shahi, Vinod K.}, title = {Advancements towards optimization of metal-organic framework-based polymer electrolyte membranes for aqueous redox flow batteries}, series = {Journal of materials chemistry : A, materials for energy and sustainability}, volume = {13}, journal = {Journal of materials chemistry : A, materials for energy and sustainability}, number = {17}, publisher = {Royal Society of Chemistry (RSC)}, address = {London}, issn = {2050-7488}, doi = {10.1039/D4TA08720H}, pages = {11952 -- 11988}, abstract = {Aqueous redox flow batteries (ARFBs) are considered a potential technology for large-scale energy storage owing to their eco-friendliness, high current density, and tuneable capacity. Polymer electrolyte membranes (PEMs) are vital components of ARFB, but they suffer from significant capacity/efficiency deterioration due to a lack of advancement in structural framing. To enhance the effectiveness of ARFBs, various membrane types have been optimized. However, the development of an efficient PEM remains a significant problem. Metal-organic frameworks (MOFs) made up of metal sites and organic linkers have gained significant scientific interest. As a result of their large surface area, adjustable pore diameters, and customized functionality, MOF-based PEMs are regarded as effective separators for ARFB. This review covers the state of the art MOF-based PEMs as ARFB separators. In recent years, significant efforts have been made to utilize the unique characteristics of MOFs as they not only improve the conductivity (attributed to their 3D channel structure) and gradient distribution in the polymer framework but also stabilize and mitigate active species cross-over by regulating the effective pore size. The aforementioned tactics can stimulate more research on energy storage technologies and provide future insight into the development and design of size-sieving separators for ARFB.}, language = {en} } @misc{JanaChauhanMuthukumaretal., author = {Jana, Sayantan and Chauhan, Nikhil and Muthukumar, Palanisamy and R{\"o}ntzsch, Lars}, title = {Transient analysis and performance prediction of a metal hydride based thermal energy storage system with Integrated cooling and heat upgradation}, series = {Heat transfer engineering : an international journal}, journal = {Heat transfer engineering : an international journal}, publisher = {Taylor \& Francis}, address = {London}, issn = {0145-7632}, doi = {10.1080/01457632.2025.2521599}, pages = {1 -- 13}, abstract = {This work embodies a numerical model development and simulation of a metal hydride-based thermal energy storage system with integrated cooling as well heat upgradation. The concept of this system is unique as it operates on thermal drive during the energy storage cycle while during the energy release cycle it is compressor-operated. The utility of the mechanical compressor in the system is two-fold i.e., one operation mode would harness cooling, and another operation mode would fetch heat upgradation. The numerical model devised is a lumped parameter model which solves for hydrogen concentration and temperature of the linked metal hydride reactors. The proposed thermal energy storage system is of 5 MJ capacity which engages tube bundle reactor settings for both high-temperature and low-temperature hydride alloys. Each energy storage and release cycles are simulated for a fixed duration of 10000 s. For a fixed heat supply and heat recovery temperatures of 623 K and 573 K, the system offered cooling coefficient of performance in the range of 1.43-1.58 at 283-293 K. Also, approximately 77\% of the energy stored at 623 K could be retrieved at 573 K. In heat upgradation operation mode, 10-30 K temperature lift was accomplished.}, language = {en} } @misc{SakkasGillungThummaretal., author = {Sakkas, Nikolaos P. and Gillung, Frank and Thummar, Krunalkumar and Abang, Roger and R{\"o}ntzsch, Lars}, title = {Advanced pressurized alkaline water electrolysis at high temperatures up to 130 °C}, series = {International journal of hydrogen energy}, volume = {149}, journal = {International journal of hydrogen energy}, publisher = {Elsevier BV}, address = {Amsterdam}, issn = {0360-3199}, doi = {10.1016/j.ijhydene.2025.150075}, pages = {1 -- 12}, abstract = {Operating alkaline water electrolysers above 100 °C improves electrolyte conductivity and reaction kinetics significantly. To examine alkaline water electrolysis in this area in more detail a high-temperature pressurized test rig is designed and constructed. Nickel (Ni) foam electrodes coated with Raney nickel (Raney Ni) or nickel manganese (NiMn) and expanded Ni mesh electrodes coated with nickel(II) oxide (NiO) are utilized and the effect of electrolyte flow rate, electrode structure, pressure and temperature variation on the cell performance at temperatures up to 130 °C and pressures up to 16 bar are investigated. At the maximum current density of 1.67 A/cm2, 110 °C and 16 bar the electrode combination of Raney Ni coated Ni foam as cathode and NiO coated expanded Ni mesh electrode as anode attain the best outcome with a cell voltage of 2.29 V. In a 70 h duration test three-dimensional (3D) Ni foam electrodes with Raney Ni cathode and NiMn anode catalyst show a moderate cell degradation of 9.26 μV/h.}, language = {en} } @misc{SampangiJarubulaElasmaretal., author = {Sampangi, Shiva Kumar and Jarubula, Charath Krishna and Elasmar, Mohamed and R{\"o}ntzsch, Lars}, title = {Advanced anion exchange membrane electrolyser with 360 cm² active cell area}, series = {EFCF 2025 : Fuel Cells, Electrolysers \& H2 Processing}, journal = {EFCF 2025 : Fuel Cells, Electrolysers \& H2 Processing}, publisher = {European Fuel Cell Forum AG}, address = {Luzern}, doi = {10.5281/zenodo.17244119}, pages = {1 -- 6}, abstract = {Anion Exchange Membrane Water Electrolysis (AEMWE) has emerged as a promising technology for generating green hydrogen, particularly using intermittent renewable energy sources. AEMWE offers a compelling opportunity for cost-effective and sustainable hydrogen production by combining the advantages of traditional alkaline water electrolysis, such as the use of abundant and low-cost catalysts, with the benefits of Proton Exchange Membrane (PEM) electrolysis, which includes membrane separation with pure or low-concentration alkaline water and operation at high current densities. However, the widespread commercialization of AEMWE remains in its early stages, with small-scale active cell areas (less than 300 cm²) and ongoing challenges related to performance and durability. Consequently, it is vital to develop high-performance, durable AEMWE cells with larger active areas to facilitate the broader adoption of this technology. This contribution presents our recent progress in AEMWE, focusing on the development of cells with an active area of up to 360 cm². In particular, we are advancing AEMWE technology to Technology Readiness Level (TRL) 5/6, incorporating precious metal-free catalysts and advanced membranes to enhance the flexibility and efficiency of hydrogen production. As part of this effort, we have designed and experimentally tested a 100 cm² AEMWE cell and conceptualized and designed a 4-kW short-stack with a total active cell area of 1800 cm², as shown in Figure. 1, for high-pressure operation at 30 bar. Our ongoing efforts includes the laboratory testing of this newly designed stack at high pressure operation and evaluating its electrochemical performance and durability up to 1,000 h continuous operation using precious metal-free electrocatalysts.}, language = {en} } @techreport{KlattPfeifferBendigetal., author = {Klatt, Matthias and Pfeiffer, Klaus and Bendig, Martin and Platta, Kristian and Matzekat, David}, title = {Betrachtungen zur Mindesterzeugung von Braunkohlekraftwerken im Kontext des Netzbetriebs}, publisher = {Brandenburgische Technische Universit{\"a}t, Fachgebiet Dezentrale Energiesysteme [u.a.]}, address = {Cottbus ; Senftenberg}, language = {de} } @misc{DanilaVollmerKunz, author = {Danila, Kevin and Vollmer, Jan and Kunz, Philip}, title = {Performance evaluation of reanalysis models for upsampling of solar irradiance and wind speed data}, series = {Renewable energy}, volume = {261}, journal = {Renewable energy}, publisher = {Elsevier BV}, address = {Amsterdam}, issn = {0960-1481}, doi = {10.1016/j.renene.2026.125301}, pages = {1 -- 13}, abstract = {The transition to renewable energy sources is a cornerstone of modern energy system transformation. Yet, the integration of solar and wind power remains challenging due to limited availability of high-resolution time series data. Accurate modeling and forecasting of renewable energy generation are essential for grid stability, and the effective deployment of technologies such as water electrolysis. However, most available datasets are provided at coarse temporal resolutions, which restricts their utility for dynamic system analysis and hinders the development of robust operational strategies. This study addresses this critical gap by evaluating the performance of reanalysis models and introducing a statistical upsampling approach that generates data with 1-min resolution from reanalysis data with 1-h resolution using a first-order Markov chain Monte Carlo method. The method is validated against measured data. The normalized root-mean-square error of the simulated data is less than 10\% and the mean intra-hour standard deviation differs from 4.8\% to 9.1\% compared to measured values for solar irradiance and wind speed. The generated data facilitates the optimization of system operation, and enhances the planning of sector-coupled infrastructures. Ultimately, this approach enables reliable integration of renewable energy despite limited data availability and thus contributes to the advancement of the sustainable energy transition.}, language = {en} } @misc{DanilaKunzRoentzsch, author = {Danila, Kevin and Kunz, Philip and R{\"o}ntzsch, Lars}, title = {Low-temperature electrolysis model optimized for improved performance in dynamic simulations}, series = {International journal of hydrogen energy}, volume = {223}, journal = {International journal of hydrogen energy}, publisher = {Elsevier BV}, address = {Amsterdam}, issn = {0360-3199}, doi = {10.1016/j.ijhydene.2026.154294}, pages = {1 -- 12}, abstract = {Traditional hydrogen production methods contribute significantly to greenhouse gas emissions, making technological change essential. Water electrolysis powered by renewable energy offers a promising route for sustainable hydrogen production. However, the variability of renewables challenges efficient electrolyzer operation, often requiring detailed simulations with long time series and high computational effort. We present a dynamic model of a low-temperature electrolyzer system optimized for computational efficiency. The model increases computational speed by a factor of 1000 compared to full-balance models while maintaining accuracy above 99\% in hydrogen prediction. The simplified model is used to investigate the benefits of modularization in large-scale hydrogen plants. Results show that modularization has a minor effect on overall output but significantly increases operational time. This extended production window can reduce the need for large-scale hydrogen storage, especially when integrated with a continuous hydrogen consumer.}, language = {en} }